Pharmacokinetics of Ceftiofur Crystalline-Free Acid in Clinically Healthy Dogs (Canis lupus familiaris)

Abstract

Economical, injectable antibiotics are beneficial when clinical manifestations of an animal model prevent the use of oral antibiotics. Ceftiofur crystalline-free acid (CCFA) is an injectable, sustained-release form of ceftiofur, a third-generation cephalosporin that is labeled for use in swine, cattle, and horses. Because CCFA is an economical, injectable antibiotic that could be of value for use in research dogs, the objective of this study was to determine the pharmacokinetic properties of CCFA in apparently healthy dogs and to determine the minimal inhibitory concentrations of ceftiofur for veterinary pathogens cultured during 2011 through 2014 from the respiratory system, integumentary system, and urinary system of dogs. The study population comprised of 5 dogs (age, 1 y; weight, 24.7 to 26.9 kg) that were deemed healthy after no abnormalities were found on physical exam, CBC analysis, and clinical chemistry panel. Each dog received CCFA at 5.0 mg/kg SC, and blood samples were collected before administration of CCFA and at 1, 4, 8, 12, 24, 36, 48, 72, 96, 120, 144, 168, 192, 216, and 240 h after injection. The maximal plasma concentration (mean ± 1 SD) of CCFA was 1.98 ± 0.40 μg/mL, time to reach maximal concentration was 22.3 ± 8.9 h, half-life was 56.6 ± 16.9 h, and AUC_0-last was 124.98 ± 18.45 μg-h/mL. The minimal inhibitory concentrations of ceftiofur ranged from ≤0.25 to ≥8.0 μg/mL; ceftiofur was most effective against Pasteurella spp., Proteus spp., and Escherichia coli haemolytica and least effective against Bordatella bronchiseptica, Enterococcus spp., and Pseudomonas aeruginosa.

In the canine laboratory animal population, injectable antibiotics are beneficial when clinical manifestations of an animal model, such as megaesophagus in Duchenne muscular dystrophy, prevent the use of oral antibiotics. Ceftiofur, a third-generation cephalosporin, is a β-lactam antibiotic that interferes with cell-wall synthesis by inactivating transpeptidase.²⁶ Ceftiofur's antimicrobial properties are time-dependent, meaning the degree of bacterial killing is determined by the duration of exposure to the drug.³ Because of their pharmacokinetic–pharmacodynamic properties, the therapeutic goal when using cephalosporins is to maintain the plasma concentration above the minimal inhibitory concentration (MIC) of target pathogens for the duration of the treatment period.^3,26

Ceftiofur crystalline-free acid (CCFA) is an extended-release injectable formulation of ceftiofur. It is approved for treating Actinobacillus pleuropneumniae, Pasteurella multocida, Haemophilus parasuis, and Streptoccus suis in swine respiratory disease;^14,32 Streptococcus equi ssp. zooepidemicus in lower respiratory tract infections of horses;¹⁷Mannheimia haemolytica, Pasteurella multocida, and Histophilus somni in bovine respiratory disease; bacterial organisms susceptible to ceftiofur in acute metritis in lactating dairy cattle (0 to 10 d postpartum);¹³ as well as the pathogens Fusobacterium necrophorum and Porphyromonas levii, which cause infectious pododermatitis in cattle.^15,31 Extralabel use of CCFA has been investigated in alpacas (Vicugna pacos), ball pythons (Python reguis), American black ducks (Anas rubripes), California sea lions (Zalophus californianus), Asian elephants (Elephas maximus), helmeted guinea fowl (Nuumida meleagris), and domestic goats (Capra aegagrus hircus),^{1,2,11,12,19,22,30} revealing broad variability in measured pharmacokinetic parameters between species. The purpose of this study was to define the pharmacokinetics properties of a single subcutaneous dose of CCFA and to determine the MIC of ceftiofur for bacterial pathogens commonly isolated from the respiratory, integumentary, and urinary systems of dogs.

Materials and Methods

Animals.

Intact adult mixed breed dogs (n = 5; age, 1.3 ± 0.05 y; weight, 25.8 ± 0.92 kg) from Marshall Farms (North Rose, NY) were used in this study. All dogs were singly housed in 4 ft by 6 ft runs with Nylabone Durachews (Nylabone, Neptune City, NJ) or Kong (The Kong Company, Golden, CO) toy enrichment at an AAALAC-accredited animal facility at the University of Missouri. Dogs were socialized and walked daily by the staff of the University of Missouri Comparative Medicine Orthopedic Laboratory. Dogs were fed Purina Pro Plan (Purina, St Louis, MO) in an amount necessary to maintain a body condition score of 5 on a scale of 9 with 5 being an ideal body condition. Dogs had unrestricted access to tap water and were housed in rooms maintained at 70 ± 2 °F with 30 to 70% relative humidity and kept under a 12:12 h light:dark cycle. All procedures performed were under an approved University of Missouri Animal Care and Use Committee Animal Protocol in accordance with the Guide for the Care and Use of Laboratory Animals,²⁰ Public Health Service policy,²⁵ and Animal Welfare Act and Regulations.⁴

Health assessment.

At 1 wk prior to the study, all dogs underwent a complete physical exam, CBC count, and serum chemistry analysis. All 5 dogs were deemed clinically healthy and were accepted into the study.

CCFA administration and sample collection.

Each dog was weighed immediately prior to drug administration. CCFA (Excede for Swine, Zoetis, Florham Park, NJ) was injected subcutaneously over the right scapula at a dose of 5.0 mg/kg. This dosage was selected in light of the recommended label dose for swine. Blood samples (5 mL each) were collected from the cephalic vein directly into a lithium heparin vacuum phlebotomy tube (Becton Dickinson, Franklin Lakes, NJ) prior to drug administration and at 1, 4, 8, 12, 24, 36, 48, 72, 96, 120, 144, 168, 192, 216, and 240 h after administration. Blood was kept on ice for as long as 60 min until processed. Samples were centrifuged for 15 min, and the plasma was divided into 1.5-mL aliquots. Plasma samples were frozen at –80 °C until analysis.

Monitoring adverse effects.

After the administration of CCFA, the injection sites were monitored for pain, erythema, swelling, and pruritus a minimum of 3 times daily on days 1 and 2. On days 3 through 10 after administration of CCFA the injection sites were monitored a minimum of once daily. In addition, the dogs’ behavior, food consumption, and fecal output were monitored daily for signs of adverse reactions.

Sample analysis.

Ceftiofur and desfuroylceftiofur metabolites in plasma samples and standards (0.5 mL) were derivitized to desfuroylceftiofur acetamide (DCA) and then underwent solid-phase extraction according to a previously described and validated method.¹⁰

Standards were prepared by spiking blank canine plasma with ceftiofur hydrochloride reference standard (Sigma–Aldrich, St Louis, MO) dissolved in methanol and diluted in water. Measurement of DCA concentrations was performed on an I Class Aquity UPLC with a Xevo/TQD mass spectrometer (Waters, Milford, MA). A linear gradient elution was performed at a flow rate of 0.2 mL/min on a C₁₈ column (Acuity BEH C₁₈ 1.7 µm 2.1 × 100 mm analytical column, Waters). The column mobile phase consisted of acetonitrile (A) and water (B) with 0.1% formic acid added to both solvents. Column conditions were 10% A:90% B at 1 min, 90% A:10% B at 2.5 min, and then returned to the initial injection condition at 3.5 min, and then were held for 3.5 min prior to the next injection. The retention time of DCA under these conditions was approximately 3 min. Column and samples were maintained at 35 °C and 25 °C, respectively, during analysis. The injection volume was 5 µL. The collision and desolvation gases used were argon and nitrogen, respectively. DCA was acquired in the positive ion mode, by using the 487 to 241 transition. Under these conditions, DCA was linear from 0.05 to 10 μg/mL. The overall lower limit of quantification was 0.05 μg/mL, and the lower limit of detection was 0.02 μg/mL, with an R² = 0.99 daily and intraday slope coefficient of variation of 3.6%.

Pharmacokinetic analysis.

For each dog, the plasma DCA concentration compared with time data were analyzed according to noncompartmental pharmacokinetics by using computer software (PK Solutions 2.0, Summit Research Services, Montrose, CO). The rate constant of the terminal phase (λ_z) was determined by linear regression of the terminal phase of the logarithmic plasma concentration compared with time curve using a minimum of 5 data points. The half-life of the terminal phase (t_1/2λz) was calculated as ln 2 divided by λ_z. The AUC was calculated by using the trapezoidal rule, with extrapolation to infinity by using C_min/λ_z, where C_min was the final measurable DCA concentration. The mean residence time was calculated as AUMC/AUC, where AUMC is the area under the first moment of the concentration–time curve. The apparent volume of distribution per fraction of dose absorbed based on the AUC (Vd_area/F) was calculated as dose divided by AUC × λ_z, where F is bioavailability). Systemic clearance per fraction of dose absorbed was calculated as dose divided by AUC. The software was also used to simulate steady-state concentrations after subcutaneous administration of CCFA at 5 mg/kg every 72, 96, 120, or 168 h.

MIC data.

The MIC of ceftiofur against canine pathogens from the respiratory, urinary, and integumentary systems were obtained from the University of Missouri Veterinary Diagnostic Laboratory submission records database from the past 3 y (1 March 2011 to 1 March 2014). Sample types were bronchoalveolar lavage, bronchial brush, and tracheobronchial aspirates for the respiratory system; urine for the urinary system; and culturette swabs for the integumentary system. MIC determinations were performed by using lyophilized microbroth dilutions (Sensititre, Oakwood Village, OH) in accordance with the guidelines of the Clinical and Laboratory Standards Institute.⁹ Dilutions tested included 0.25, 0.5, 1, 2, 4, and 8 µg/mL. Quality control strains used to validate the assay at weekly intervals included Staphylococcus aureus ATCC 29213, Enterococcus faecalis ATCC 29212, Escherichia coli ATCC 25922, and Pseudomonas aeruginosa ATCC 27853. In all instances, MIC obtained with the control strains were within the reference range proposed by the Clinical and Laboratory Standards Institute.

Results

CCFA was well tolerated by all 5 dogs throughout the study period. No changes in appetite, behavior, or stool consistency were observed, and there were no adverse reactions at the injection sites. After subcutaneous injection of CCFA, the plasma DCA concentrations in 4 of the 5 dogs remained detectable at all time points (Figure 1). The DCA plasma concentrations were below the limit of quantification (0.05 µg/mL) for 1 dog at 168 and 192 h after injection, and DCA plasma concentrations were below the limit of detection (0.02 µg/mL) for this dog at 216 and 240 h after injection. The mean C_max of CCFA was 1.98 ± 0.40 µg/mL, the half-life was 56.58 ± 16.9 h, the AUC_0-last was 125.0 ± 18.45 μg×h/mL, the overall mean residence time was 74.2 ± 17.6 h, the Vd/F was 3.05 ± 0.59 L/kg, the mean systemic clearance per fraction absorbed was 39.1 ± 6.7 mL/h/kg, and the λ_z was 0.01 ± 0.011/h (Table 1).

Figure 1.

Plasma concentration of desfuroulceftiofur acetamide (DCA) from each dog after subcutaneous administration of CCFA at a dose of 5 mg/kg. The asterix (*) denotes that for dog 4, time points 216 and 240 h after administration were below the limit of detection. Also shown is the mean (error bars, ± 1 SD) DCA concentration of all 5 dogs.

Table 1.

Pharmacokinetic variables after administration of CCFA to dogs at a dose of 5 mg/kg SC

Dog no.	Cmax (μg/mL)	Tmax (h)	t1/2λz	AUC0-last (μg×h/mL)	MRT (h)	VDarea/F (L/kg)	Cl/F (mL/h/kg)	λz (1/h)
1	1.30	36	50.48	131.5	89.4	2.63	36.2	0.014
2	1.93	24	59.10	127.1	82.1	3.21	37.2	0.012
3	1.88	8	61.37	111.2	69.8	3.76	42.5	0.011
4	2.42	24	29.90	100.6	41.8	2.14	49.7	0.023
5	2.36	24	82.07	154.5	87.7	3.53	29.8	0.008
Mean	1.98	23.2	56.58	125.0	74.2	3.05	39.1	0.010
1 SD	0.40	8.91	16.90	18.45	17.6	0.59	6.67	0.010

CL/F, clearance per fraction of dose absorbed; T_max, time to maximal plasma concentration

The pharmacokinetic predictions for multiple doses of CCFA are outlined in Table 2. The concentrations maintained varied depending on the dosing interval, with maximal steady-state concentrations of 2.22 to 1.42 µg/mL, minimal concentrations of 0.92 to 0.18 µg/mL, and mean concentrations of 1.36 to 0.62 µg/mL.

Table 2.

Predicted steady-state maximal (max), minimal (min), and average (ave) plasma concentrations (mean ± 1 SD) for CCFA administered to dogs at 5 mg/kg SC every 72, 96, 120, or 168 h

Dosing interval (h)	Concentration (μg/mL)
	Cssmax	Cssmin	Cssave
72	2.22 ± 0.27	0.92 ± 0.34	1.36 ± 0.56
96	1.84 ± 0.60	0.56 ± 0.22	1.12 ± 0.34
120	1.64 ± 0.56	0.38 ± 0.16	0.88 ± 0.30
168	1.42 ± 0.50	0.18 ± 0.12	0.62 ± 0.22

The diagnostic lab obtained MIC values for a total of 59 isolates from the respiratory tract, 285 isolates from skin and wounds, and 852 isolates from the urinary tract from March 2011 to March 2014. Figure 2 shows the MIC distribution by target organ system, except for Bordetella bronchiseptica, Enterococcus spp., and Pseudomonas aeruginosa, because these bacteria are known to be resistant to cephalosporins. Bordetella bronchiseptica and E. coli spp. were the 2 bacterial pathogens recovered most often from the respiratory tract (Table 3). Ceftiofur was most active against Pasteurella multocida ss multocida followed by E. coli spp., given that 89% of E coli spp. had an MIC of 1.0 µg/mL. Ceftiofur was not active against Bordetella bronchiseptica (Table 3). Staphylococcus spp. were the bacterial pathogens recovered most often from wounds (Table 4). For infected wounds, ceftiofur was most active against Proteus spp. (Table 4) followed by E. coli spp., with 86% of the isolates having MIC of 1.0 µg/mL. Ceftiofur was not active against Pseudomonas aeruginosa (Table 4). From the urinary tract, E coli was the most commonly isolated bacterial pathogen, followed by Staphylococcus intermedius (Table 5); 86% of E. coli isolates had an MIC of 1 µg/mL. Ceftiofur was most active against Proteus mirabilis and E. coli haemolytica but was inactive against Enterococcus faecalis, Enterococcus faecium, and Pseudomonas aeruginosa (Table 5).

Figure 2.

The MIC distribution of all organisms except for Bordetella bronchiseptica, Enterococcus spp., and Pseudomonas aeruginosa isolated by the diagnostic lab from 1 March 2011 to 1 March 2014.

Table 3.

Respiratory tract pathogens, with the total number of isolates for each identified bacteria

	No. of isolates	MIC50	MIC90	MIC range
Bordetella bronchiseptica	20	≥8.0	≥8.0	≥8.0
Enterobacter aerogenes	1			1.0
Escherichia coli spp	18	0.5	≥8.0	≤0.25 to ≥8.0
Klebsiella pneumonia ss pneumonia	9	1.0	≥8.0	0.5 to ≥8.0
Pasteurella multocida ss multocida	6	≤0.25	≤0.25	≤0.25
Pseudomonas aeruginosa	5	2.0	≥8.0	0.5 to ≥8.0
All respiratory isolates	59	1.0	≥8.0	≤0.25 to ≥8.0

Table 4.

Integumentary pathogens, with the total number of isolates for each identified bacteria

	No. of isolates	MIC50	MIC90	MIC range
Escherichia coli	28	0.5	≥8.0	≤ 0.25 to ≥8.0
Proteus spp.	14	≤0.25	≤0.25	≤ 0.25 to ≥8.0
Pseudomonas aeruginosa	23	≥8.0	≥8.0	4.0 to ≥8.0
Staphylococcus epidermidis	14	0.5	2.0	≤ 0.25 to ≥8.0
Staphylococcus intermedius	181	≤0.25	4.0	≤ 0.25 to ≥8.0
Other Staphylococcus spp	25	≤0.25	2.0	≤ 0.25 to 4.0
All wound isolates	285	≤0.25	≥8.0	≤ 0.25 to ≥8.0

Table 5.

Urinary tract pathogens, with the total number of isolates for each identified bacteria

	No. of isolates	MIC50	MIC90	MIC range
Enterobacter aerogenes	12	1.0	≥8.0	1.0 to ≥8.0
Enterococcus faecalis	88	≥8.0	≥8.0	0.5 to ≥8.0
Enterococcus faecium	36	≥8.0	≥8.0	≤ 0.25 to ≥8.0
Escherichia coli	372	0.5	≥8.0	≤ 0.25 to ≥8.0
Escherichia coli haemolytic	68	0.5	0.5	≤ 0.25 to ≥8.0
Klebsiella spp	30	0.5	2.0	0.5 to ≥8.0
Pasteurella multocida ss multocida	1			≤0.25
Proteus mirabilis	74	≤0.25	0.5	≤ 0.25 to ≥8.0
Pseudomonas aeruginosa	30	≥8.0	≥8.0	≥8.0
Staphylococcus intermedius	141	≤0.25	2.0	≤ 0.25 to ≥8.0
All urinary isolates	852	0.5	≥8.0	≤ 0.25 to ≥8.0

Discussion

At our institution, aspiration pneumonia can occur in our Duchenne Muscular Dystrophy canine model due to the clinical manifestations of the disease; therefore we need an economically feasible, injectable antibiotic to treat the pneumonia. We investigated using cephalosporins given that broad-spectrum antibiotics are recommended for treating pneumonia.⁷ Currently, there are 2 sustained release injectable forms of cephalosporins labeled for use in veterinary species: cefovecin sodium and CCFA. Cefovecin sodium is the only long-acting subcutaneous injectable antibiotic approved for dogs. Cefovecin is a third-generation cephalosporin labeled for the treatment of skin infections caused by susceptible strains of S. intermedius and Streptococcus canis (group G). Therapeutic drug concentrations are maintained for 7 d for S. intermedius (MIC₉₀, 0.25 μg/mL) and 14 d for S. canis (group G; MIC₉₀, ≤0.06 μg/mL) with a maximal treatment dosage of 2 injections.¹⁶ Because using cefovecin sodium to treat bacterial infections not caused by S. intermedius or S. canis (group G) is considered to be ‘off label,’ we chose to pursue using CCFA off label because it is economically more viable than is cefovecin and has shown to be effective both against respiratory pathogens and soft-tissue pathogens in other mammalian species.

Before using CCFA off label in dogs, it is important to understand the pharmacokinetics of CCFA in this species, because the most important factor when determining the efficacy of ceftiofur, a β-lactam antibiotic, is the duration of time that the serum concentrations of the drug are maintained above the MIC.⁵ When ceftiofur is administered to dogs, it is rapidly metabolized into metabolites, with DCA being the primary metabolite.^8,21,28

Because DCA is the active drug in the dog, it is important to understand that the MIC₅₀, MIC₉₀ and MIC range obtained from the diagnostic lab are not for DCA but rather were based on in vitro susceptibility assays against ceftiofur. The MIC values obtained for many gram-negative organisms including E. coli spp., Pasteurella spp., Salmonella spp., and Streptococci spp. were the same for ceftiofur and DCA.²⁸ However, the activity of DCA was lower than that for ceftiofur against several gram-negative organisms, including Pseudomonas aeruginosa and Enterobacter faecium.²¹ In addition, the MIC for DCA against gram-positive Staphylococcus spp. were 2 to 3 serial-dilution increases from that for ceftiofur.²⁸ Here we evaluated a total of 6 gram-negative canine bacterial species isolated from the respiratory tract, with a cumulative MIC₅₀ that could be achieved for 48 h after the injection of a single 5.0-mg/kg SC dose of CCFA. At 96 h after administration, the plasma concentrations were maintained above the MIC₅₀ for E. coli spp. and above the MIC₉₀ for Pasteurella multocida ss multocida respiratory tract isolates. A single dose of CCFA was ineffective for achieving the MIC₅₀ for Pseudomonas aeruginosa, and no Bordetella bronchiseptica isolates were susceptible to ceftiofur, which was expected due to both bacteria having documented resistance.²⁹ Given that we had only one isolate of Enterobacter aerogenes, whether ceftiofur is an appropriate antibiotic for treating this organism remains unknown.

When determining an appropriate dosing interval, the goal should be to maintain plasma concentrations of ceftiofur above the MIC of an organism for approximately 50% of the dosing interval.²⁴ Maintaining the plasma concentrations markedly above 50% of the dosing interval does not provide marked additional benefit because of the plateau in the bacteriologic cure rate;^23,24 therefore, with pharmacokinetic predictions, we can use the average steady-state plasma concentration of DCA to guide the timing of redosing. In the current context, a 4-d dosing interval would maintain an average plasma concentration of 1.12 μg/mL, which exceeds the MIC₅₀ for Klebsiella pneumonia ss pneumoniae, and redosing every 5 to 7 d achieves an average plasma concentration of 0.88 to 0.62 μg/mL, which exceeds the MIC₅₀ of E. coli spp. and Pasteurella multocida ss multocida. Finding a cumulative MIC₅₀ for respiratory isolates of 1.0 μg/mL suggests that CCFA may not always be the most appropriate single therapeutic agent to select for the treatment of respiratory infections.

In addition to respiratory infections, cephalosporins are frequently used to treat infected wounds and urinary tract infections in veterinary medicine. In the laboratory animal field, we can often encounter bacterial skin infections in immunosuppressed animals. The most commonly cultured organism from skin wounds was S. intermedius, with 181 isolates identified. Interestingly, the diagnostic lab reported an MIC₉₀ of 4.0 μg/mL, whereas the S. intermedius MIC₉₀ reported in the package insert for cefovecin sodium was ≤0.25 μg/mL.¹⁶ Our data indicate that we would not achieve a MIC₉₀ for S. intermedius; however we could reach the MIC₉₀ reported by the drug manufacture at 120 h after the injection of CCFA, with a DCA concentration that is maintained above 0.25 μg/mL. This wide disparity in MIC values highlights the benefit to veterinarians of culturing the isolated organism and determining its specific MIC. However when evaluating MIC for ceftiofur, we must take into consideration that DCA is 2 to 3 serial dilutions less active against Staphylococcus spp. than is ceftiofur,²⁸ and we therefore can infer that the DCA concentration would be maintained above an MIC₅₀ for only 48 h. This situation highlights how ceftiofur is often an inappropriate antibiotic for treating Staphylococcus spp. infections because the activity of DCA is significantly lower than that of ceftiofur.²⁸ However, in light of the MIC₅₀ for S. intermedius and other Staphylococcus spp., our pharmacokinetic predictions indicate that a 4-d dosing interval would maintain an average plasma concentration of 1.12 μg/mL, which would exceed the reported MIC₅₀ of ≤0.25 μg/mL. For the other wound isolates, the DCA concentrations reached MIC₉₀ concentrations for Proteus spp. and MIC₅₀ for E. coli spp.

Cephalosporins primarily undergo renal excretion, leading to high drug concentrations in the urine and making them good choices for urinary tract infections.²⁷ Given this fact, we hypothesize that urinary levels are at least equivalent to the plasma levels of CCFA. Therefore, the MIC₅₀ of all cultured bacteria except Enterococcus faecalis, Enterococcus faecium, and Pseudomonas aeruginosa could be maintained for at least 48 h after the injection of CCFA. These results were expected, given that cephalosporins are known to lack activity against Enterococcus species and Pseudomonas spp.^6,27 For the urinary bacterial isolates, 75% had an MIC 1.0 μg/mL, but the percentage of urinary tract bacteria requiring this MIC may be artificially high due to the common veterinary practice of first treating urinary tract infections without culturing, and only samples of cases that are resistant to treatment or from frequently reoccurring urinary tract infections typically are submitted for culture. It is important to note that a limitation of this study was that the CCFA concentration of the urine was not measured; such a study would need to be undertaken to determine whether the urinary concentration of CCFA is in fact similar to that of the plasma concentration. This information would allow the interpretation of MIC data from urinary tract isolates and to allow predictions of appropriate redosing intervals.

Additional studies should be done to confirm that the pharmacokinetic predictions we obtained are accurate and to determine whether multiple doses cause any adverse reactions. Subcutaneous administration of CCFA at a 4-d interval reportedly caused injection site reactions in adult horses,¹⁸ likely because the oil-based suspension of CCFA is more irritating than are ceftiofur aqueous solutions. Furthermore, another study should investigate whether an increased dose increases the circulating concentration of DCA in the blood and whether the duration that DCA remains above the MIC₉₀ of commonly isolated canine pathogens can be extended. In addition, a dose study would be beneficial, because a dose of 5.0 mg/kg takes 4 h to achieve 0.96 µg/mL and a higher initial dose might result in a more rapid onset of action. Because the dose selected for the current study resulted in only low plasma levels of DCA within the first few hours after injection of CCFA, an intravenous alternative might be more suitable when immediate antimicrobial therapy is indicated.

In conclusion, our study demonstrated that CCFA could be maintained above the MIC₅₀ and MIC₉₀ for various isolates cultured from the respiratory, integumentary or urinary tract. It is essential to consider the organ system requiring treatment and the pathogens that likely are present to determine whether CCFA or another antibiotic would be the most appropriate therapeutic agent.